One way of spot plating a strip of metal is to guide the strip through a plating head. The strip is intermittently advanced a certain distance. When it stops, the plating head clamps the strip so that plating electrolyte may be washed against the surface of the strip from passageways in the plating head. In the prior art, a compliant masking material is mounted on the plating head so as to define the exact areas on the strip that are to be plated. The mask has openings of precise size, shape, and location so that electrolyte is channeled from the plating head passageways only to areas on the strip that are exposed in these openings. However, if the strip is to be plated in the exact right spot, it is necessary that the strip always be positioned correctly relative to the mask when the strip comes to rest. To accomplish this in the prior art, it was necessary to have some mechanism to ascertain the relative position of the strip and the plating head and additional mechanisms to move either the strip or the plating head so as to achieve the correct position.
An example of such a set of mechanisms may be found in U.S. patent application Ser. No. 06/280,597, filed July 6, 1981 by Carl E. Bernardi, entitled Automatic Self-Adjusting Processing apparatus, and assigned to the assignee of this application. It is therein described how the quantity of air passing through indexing holes in the strips of metal is used to determine the misalignment of the strip. This information is then used by a control mechanism that mechanically adjusts the plating head back and forth until the correct location is established. Such a system is accurate but complex and expensive. The present invention is much less complicated and thus less expensive.